Automatic control for an air conditioning system

ABSTRACT

A CONTROL CIRCUIT FOR AN AIR CONDITIONING SYSTEM INCLUDING A REFRIGERATION UNIT COMPRISING A MOTOR-DRIVEN COMPRESSOR, A CONDENSER, AN EVAPORATOR, EXPANSION MEANS, AND MEANS TO SUPPLY HEAT EXCHANGE MEDIA TO THE CONDENSER AND EVAPORATOR OF SAID REFRIGERATION UNIT. A PRESSURE-ACTUATED SWITCH WILL PREVENT THE CIRCUIT SUPPLYING POWER TO OPERATE THE COMPRESSOR MOTOR FROM BEING ENERGIZED IF THE PRESSURE DIFFERENTIAL BETWEEN THE SUCTION SIDE OF THE COMPRESSOR AND DISCHARGE SIDE OF THE COMPRESSOR EXCEEDS A PREDETERMINED POINT. MEANS RESPONSIVE TO A THERMAL   CONDITION OF THE AREA BEING SERVED BY THE SYSTEM WILL ENERGIZE THE HEAT EXCHANGE MEDIUM SUPPLY MEANS TO THE CONDENSER EVEN THROUGH THE COMPRESSOR MAY BE INOPERABLE BECAUSE OF AN UNSATISFACTORY PRESSURE DIFFERENTIAL. THE FLOW OF HEAT EXCHANGE MEDIUM WILL SUBSTANTIALLY EQUALIZE THE PRESSURES ENABLING THE COMPRESSOR CIRCUIT TO BE COMPLETED.

Feb. 16, 1971 V. T. BARRY AUTOMATIC CONTROL FOR AN AIR CONDITIONING SYSTEM Filed Dec. 30, 1968 2 Sheets-Sheet 1 FIG. I

FIG. 2

INVENTOR.

VINCENT T. BARRY.

ATTORNEY.

Feb. 16', '1971 v. T. BARRY 3,563,048

-AUTOMATIC CONTROL FOR AN AIR CONDITIONING SYSTEM Filed Dec. 30,1968 2 Sheets-Sheet z 39 l2 4- M 44 V-\ 4| 42 2 30 IL 3 3 1 34 z 4 4O I p 35 l i I '51 1 :g '1 26 2T 8: 21 E 1? r3 IN VENTOR.

ATTORNEY.

United States Patent Olfice 3,563,048 Patented Feb. 16, 1971 3,563,048 AUTOMATIC CONTROL FOR AN AIR CONDITIONING SYSTEM Vincent T. Barry, Camillus, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Dec. 30, 1968, Ser. No. 787,888

Int. Cl. F25b 1/00 US. Cl. 62-115 8 Claims ABSTRACT OF THE DISCLOSURE A control circuit for an air conditioning system including a refrigeration unit comprising a motor-driven compressor, a condenser, an evaporator, expansion means, and means to supply heat exchange media to the condenser and evaporator of said refrigeration unit. A pressure-actuated switch will prevent the circuit supplying power to operate the compressor motor from being energized if the pressure differential between the suction side of the compressor and discharge side of the compressor exceeds a. predetermined point. Means responsive to a thermal condition of the area being served by the system will energize the heat exchange medium supply means to the condenser even though the compressor may be inoperable because of an unsatisfactory pressure differential. The flow of heat exchange medium will substantially equalize the pressures enabling the compressor circuit to be completed.

BACKGROUND OF THE INVENTION This invention relates to a novel control to be used with an air conditioning system including a refrigeration unit, and more particularly, with refrigeration units havin g motor-driven compressors.

A substantial number of the motor-driven refrigerant compressors in use have low starting torque and high initial current characteristics. Thus, if high starting torque is required for certain starting conditions, an overload relay usually provided in the compressor control circuit 'will prevent the compressor motor from becoming operable. However, an overload relay is designed as a safety device and not as a system controller. Frequent operation of the overload relay due to high starting loads will cause the relay contact to burn out. With the overload relay inoperable, it is possible that the compressor motor will burn out, terminating the use of the air conditioning system and necessitating expensive replacements.

Conditions which produce high starting torque are many and varied. A large number of the air conditioning systems in use locate the condenser at points where it is exposed to heat, either from natural or man-made sources. The air conditioning system, during a time when the compressor is off, is affected by this heat. This heat will increase the pressure and temperature of the refrigerant particularly in the high pressure side of the machine. This incease in refrigerant temperature and pressure increases the load against which the compressor operates particularly when initially energized, therefore requiring starting torque above the characteristic of the compressor motor.

Secondly, many systems utilize a manual operating switch. It is quite a frequent occurrence for one person to manually deenergize an air conditioning system and then leave the area. A second person then rest-arts the system before the high pressure differential between the high and low sides of the refrigeration unit, produced during the operation of the unit, has been reduced to a satisfactory level. Again a situation occurs where the compressor is being forced to start against a high initial load.

Another situation involving high starting torque might occur with an automatic thermally actuated switch. Similar to rapid manual starting, a thermal switch may restart an air conditioning system before the high pressure differential between the suction and the discharge sides of the refrigeration circuit has been substantially eliminated.

Previous attempts have been made to solve the problems discussed above. A much used and satisfactory control is that in which provision is made for the prevention of compressor motor energization until the passage of a predetermined period of time. This action is often accomplished by employing time delay devices or their equivalent.

This system is useful under most conditions. However, especially when the condenser is exposed to high heat concentrations, a definite time delay may not be as sensitive a control as desired. Under such conditions, depending upon the predetermined time interval, the pressure differential may not have been substantially eliminated before the compressor can be restarted.

Another problem with the definite time delay period would be just the opposite from that previously discussed. Sometimes it would be highly desirable to restart an air conditioning system at an interval of time less than that chosen to control restarting. With a definite time delay, this is impossible, even though the pressure differential has been substantially reduced.

The object of the present invention is to alleviate some of the problems discussed herein by preventing energization of the compressor motor during that period of time when the pressure differential exceeds a predetermined amount. Secondly, means are utilized to reduce the period of time in which the pressure differential will be reduced to a predetermined level selected to avoid the above-described problems inherent in high load starting.

SUMMARY OF THE INVENTION The present invention pertains to a control for a refrigeration cycle which utilizes pressure-responsive means to prevent a compressor motor from starting or restarting until the pressure differential between the high and low sides of the cycle is compatible with favorable starting load characteristics and is concurrently operable to effect reduction of the undesirable pressure relationship in a novel and efficient manner. The invention herein disclosed is designed as a system controller, not to be operable during the normal operation of the refrigeration circuit. Therefore, bypass means are included in the invention to make the pressure-responsive means inoperable when the refrigeration unit, including the compressor, is operational.

Means are utilized to activate the heat exchange medium supply means to the condensing coil and evaporator coil of the refrigeration system, even though the compressor is inoperable. A first embodiment of the invention has a thermal-activated switch automatically starting the refrigeration unit when the area being served requires cooling. Even though the pressure-responsive means may prevent the compressor motor from becoming energized, the heat exchange medium supply means Will commence operation when the thermal switch closes.

Supplying the heat exchange medium to the condenser and evaporator when the pressure differential has exceeded a predetermined point will substantially reduce the time in which the pressure differential will decrease to a satisfactory level, thereby permitting the compressor motor to become energized more rapidly in response to the cooling demands of the area being served by the refrigeration unit.

A second embodiment of the invention has the pressure-responsive means, not only preventing the compressor motor from becoming operable until the predetermined pressure differential is established, but also controlling the operation of the heat exchange medium supply means so that the supply means will become operable when a pressure condition sufficient to keep the compressor from becoming operable has been reached. Thus, the

heat exchange medium supply means may commence operation even if the thermally actuated switch has not been activated. This in turn will further reduce the time in which the presure differential will decrease to a satis factory point permitting energization of the compressor motor.

, A further refinement of the invention has the heat exchange medium supply means actuated in response to the temperature of the refrigerant in the condenser. Again, the 'energization of the heat exchange medium supply means may take place prior to the closure of the thermally activated switch.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates schematically a type of air conditioning apparatus to which the present invention applies, and a wiring diagram of a preferred form of the air conditioning system control serving as the subject of this invention.

FIG. 2 shows a modification of the invention in which the refrigeration unit heat exchange medium supply means will be activated in response to a refrigeration unit pressure condition regardless of the area thermal condition.

FIG. 3 shows a further refinement of the invention in which the heat exchange medium supply means will be activated in response to a temperature condition of the refrigeration unit regardless of the temperature condition of the area being served by the refrigeration unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, and in particular to FIG. 1, there is schematically shown an air conditioning system employing a refrigeration unit incorporating a control arrangement of the invention herein disclosed. The refrigeration unit disclosed is representative of a refrigeration unit utilized in window mounted room air conditioners. An outdoor heat exchange coil or condenser is connected by means of line 11 with the discharge side of a suitable refrigerant compression mechanism, for example, a reciprocating type compressor 12. The gaseous refrigerant produced in compressor 12 subsequently flows through outdoor coil 10 and is condensed by ambient air routed over the surface of the condenser 10 by outdoor fan 13. Liquid refrigerant formed in coil 10 fiows through line 14, thermal expansion valve 15, and line 16 to indoor coil or evaporator 17. It is understood that other suitable expansion devices, as a capillary tube, may be employed in place of expansion valve 15. The thermal expansion valve in conjunction with compressor 12 separates the refrigeration system into a high pressure side and a low pressure side.

Liquid refrigerant in indoor heat exchange coil or evaporator 17 is converted to vaporous refrigerant as it extracts heat from the medium, for example, air passed over its surface by indoor fan 18. The cooled air is thereafter passed to the area being conditioned by suitable means such as grilles or vents (not shown). V-aporous refrigerant from coil 17 flows via suction line 19 to compressor 12 to complete the refrigerant flow cycle.

Again, referring to FIG. 1, a preferred form of the control circuit for the refrigeration unit hereinabove described is schematically shown. A suitable source of electric power is represented by lines L and L connected to a primary winding 24 of a transformer 23. It is understood that -a polyphase source of electrical power may be employed if the circuit is suitably modified.

The secondary winding 25 of the transformer 23 is connected in series with a switch 26, responsive to the temperature of air circulating in the area being served by the equipment. When thermally actuated switch 26 is closed, current is supplied to control relay 27. Energization of control relay 27 closes normally open switches 29 and 30. Once switch 29 has been closed, fan motors 20 and 21 are energized, thereby actuating outdoor fan 13 and indoor fan 18 respectively. The closure of switch 30 supplies current through normally closed switches 31, 32, 33 and 34 to compressor contactor coil 35. Energization of the compressor contactor coil 35 closes normally open switches 36 and 40. Closure of normally open switch 36 connects compressor motor 22 across lines L and L thereby starting the compressor 12. Normally closed switches 31, 32 and 33 are safety devices; respectively a high pressure cutout, a low pressure cutout, and a motor overload cutout. Other safety devices known to the art, such as low oil pressure cutout, may also be used. The occurrence of the condition protected against will open the particular switch, thereby either preventing the compressor motor from starting, or stopping the compressor motor during the normal operation of the system.

Controlling the operation of normally closed switch 34, in series with coil 35, is pressure-actuated mechanism 37. The mechanism is responsive to the suction and discharge pressures generated by the refrigerant in the refrigeration system. The mechanism illustrated schematically can be comprised of an outer shell 41. Disposed within the shell 41 is a diaphragm 42 extending horizontally so that the interior of the shell is divided into two equal spaces. A compression spring 43 is placed in the space 44 above the diaphragm 42. Conduit 39 connects the upper space 44 of the mechanism 37 with the compressor suction line 19, so that compression suction pressure is present on the top surface of the diaphragm 42. Conduit 38 transmits refrigerant discharge pressure into the bottom space 45 of the shell, the discharge pressure operating against the bottom surface of the diaphragm. Thus, it is readily apparent that mechanism 37 is a differential pressure-responsive mechanism; that is, the mechanism will become operable when a predetermined pressure differential between the discharge and suction pressures of the refrigeration system has been exceeded. Compression spring 43 aids the suction pressure in neutralizing the pressure asserted upon the diaphragm by the discharge pressure. When the mechanism 37 is actuated, normally closed contact 34 is opened. Other pressure-responsive mechanisms known to the art may be used to control the operation of normally closed switch 34.

Assume that the compressor is in operation. Thus, normally open switch 40 has been closed due to the compressor contactor coil 35 having been energized. Closure of switch 40 completes a circuit bypassing switch 34 through lines 46 and 48. It is therefore apparent that, although during the normal operation of the compressor 12, mechanism 37 may open switch 34, the opening Will not have an effect upon the operation of the refrigeration system in general and the compressor motor 22 in particular, which at this stage will be governed by the thermal condition in the area. Assume the compressor has been stopped due to the satisfaction of the thermal load, thereby opening thermal switch 26, or due to the opening of any of the normally closed switches 31, 32 or 33 for any of the reasons previously explained above. Compressor contactor coil 35 is deenergized, resulting in switch 40 returning to its normally open position.

With the bypass circuit around switch 34 now inoperative, it is therefore necessary for switch 34 to be in its normally closed position before the compressor motor 22 can restart. As previously stated, switch 34 will be opened if the pressure difierential between the high and low sides of the refrigeration system has exceeded the predetermined point.

It is highly desirable that the compressor 12 be kept inoperative while the high pressure differential is in existence. A large pressure differential between the high and low sides of a refrigeration system will increase the starting load on the compressor motor 22, thereby increasing the current required to start the compressor motor. A high initial current for a long period produces concomitant problems such as higher operating costs,

possibilities of windings burning out, and a higher manufacturing cost for the compressor motor due to the extra components required to handle the problems involved in coping with large starting torque.

Switch 34 will remain open until the pressure differential has been reduced to tolerable limits, thereby decreasing the starting load on the compressor motor and concurrently decreasing the time required to start the compressor motor. The circuit described while protecting the compressor motor against damage due to high starting torque conditions has an additional feature in that it is operable to correct the pressure imbalance and thus enables the equipment to become operative in a more efficient manner than heretofore known.

Assume now that switch 34 is in its open position as would be the case when an undesirable pressure differential occurs. If switch 26 were to close due to an increase in the thermal load in the area being served, control relay 27 Will be energized as before, closing switches 29 and 30. Even though compressor motor 22 will not start, fan motors 20 and 21 will be placed in operation, thereby routing ambient air over the condenser and evaporator 17. The passage of the ambient air over the heat exchangers in the absence of compressor operation will reduce the pressure differential between the high and low sides, thereby reducing the starting load and closing switch 34, thus enabling the compressor motor to commence operation in a relatively short period of time. The pressure differential is substantially eliminated by passing relatively cold ambient air in heat exchange relation with the relatively high pressure, high temperature refrigerant in the condenser, thereby reducing the temperature and pressure of the refrigerant located on the compressor discharge side. Secondly, the relatively warm ambient air passing in heat exchange relation with relatively low temperature, low pressure refrigerant in the evaporator raises the temperature and pressure of the refrigerant, thus increasing the suction pressure. When the pressure differential has been reduced to the predetermined point, switch 34 will close, thereby placing compressor motor 22 in operation.

Referring now to FIG. 2, there is disclosed a modified embodiment of the invention. Like numerals will refer to like parts.

In the embodiment represented by FIG. 2, pressureresponsive mechanism 37 will have a dual function. Not only will it be controlling normally closed switch 34, but it will also be controlling the operation of normally open switch 50. Normally open switch 50, when closed, will place fan motors and 21 in operation. Thus, it is apparent that normally open switch 50 will close when the pressure-responsive mechanism 37 opens switch 34. Operation of switch 50 in the manner described will energize the indoor and outdoor fans 13 and 18 even if thermally activated switch 26 has not closed. This in turn will curtail the time required to start the compressor motor 22 since operation of the fans 13 and 18 will close switch 34 in the manner previously described. Furthermore, the fan motors 20 and 21 will remain operative after the thermally activated switch 26 has been opened since normal operation of the refrigeration unit will create a high pressure differential. Operating the fans at this time will also decrease the pressure differential as desired.

During normal operation of the refrigeration unit, fan motors 20 and 21 will be controlled, as previously described, by the closure of switch 29 in response to thermally activated switch 26. Additionally, if for any reason switch 50 were to become inoperative, fan motors 20 and 21 may still commence operation prior to the energization of the compressor 12, in the manner hereinabove described, in response to thermally activated switch 26.

Referring now to FIG. 3, a further refinement of the 6 present invention is shown. Again, like numerals will refer to like parts.

As shown by this embodiment, the fan motors 20 and 21 will commence operating prior to thermally activated switch 26 closing, if normally open switch 51 closes. Normally open switch 51 is also thermally actuated. The switch is actuated in response to the temperature of the refrigerant in the high side of the refrigeration unit. If,

during the period of time when the refrigeration unit is inoperable, the condenser were to absorb large quantities of heat, the temperature of the refrigerant contained therein will increase. This increase in temperature will also increase the refrigerant pressure, thereby actuating mechanism 37 and opening normally closed switch 34. By having normally open switch 51 responsive to the increase in refrigerant temperature, it will be possible to energize fan motors 20 and 21 regardless of the operation of thermally activated switch 26. This in turn will decrease the pressure differential between the high and low sides of the refrigeration unit allowing normally closed switch 34 to resume its closed position, thereby energizing the compressor motor 22 immediately when the area being served by the refrigeration unit requires cooling. Also, since normal operation of the unit increases the refrigerant temperature, the fan motors 20 and 21 will remain operative even after the thermally responsive switch 26 has opened, thereby reducing the temperature and pressure of the refrigerant to tolerable levels to per mit reenergization of the compressor motor 22 when required.

During normal operation of the refrigeration unit, the fan motors 20 and 21 will be controlled by thermally actuated switch 26. If switch 51 were to fail, the fan motors 20 and 21 will still commence operating in response to thermally activated switch 26, even though pressure differential mechanism 37 has opened normally closed switch 34, thereby preventing the compressor 12 from becoming operable.

It is not an essential requisite for the proper operation of this invention that the indoor fan 18 be made operable when the pressure differential is being substantially eliminated. Therefore, it is within the scope of this invention for only the outdoor fan 13 to be activated when pressure differential reduction is desired.

Also, it should be understood that instead of a pressure differential mechanism controlling the energization of the compressor motor, a pressure mechanism solely responsive to the pressure of the discharge side of the refrigeration circuit may be utilized. Furthermore, such a pressureresponsive mechanism will be considered as falling within the meaning of the term pressure differential as used herein.

While I have described and illustrated preferred embodiments of my invention, it will be understood that my invention is not limited thereto, since it may be otherwise embodied within the scope of the following claims.

I claim:

1. A method of operating an air conditioning system including a refrigeration unit having a motor-driven compressor, a condenser, an evaporator, means to circulate eat exchange media over said condenser and said evaporator, and expansion means, said expansion means and said compressor defining a high pressure side and a low pressure side for the refrigeration cycle, comprising the steps of:

(i) circulating a refrigerant through said refrigeration unit by energization of said compressor, as a heat exchange medium is circulated over said condenser and said evaporator, in response to a predetermined area thermal condition and a predetermined refrigeration unit pressure condition;

(ii) terminating the operation of said air condntioning system upon satisfaction of a predetermined area thermal condition;

(iii) thereafter passing a heat exchange medium in heat 7 exchange relation with the condenser of said air conditioning system while said compressor is inoperable, in response to a predetermined thermal condition within the area being conditioned, thereby reducing the temperature and pressure of said refrigerant in said condenser and substantially eliminating the pressure differential between the high and low sides of said system; and

(iv) subsequently energizing the compressor of said air conditioning system when the pressure differential between the high and low sides of said air conditioning system has been reduced to a predetermined point by the action of the heat exchange medium passing over the condenser.

2. A method of operating an air conditioning system in accordance with claim 1 wherein a heat exchange medium will be passed in heat exchange relation with said evaporator simultaneously with a heat exchange medium being passed in heat exchange relation with said condenser while said compressor is inoperable.

3. A method of operating an air conidtioning system in accordance with claim 1 wherein said heat exchange medium will be supplied to said condenser in response to a predetermined pressure condition within said refrigeration unit, while said compressor is inoperable and at a time when the thermal condition of the area being served does not require operation of the refrigeration unit.

4. A method of operating an air conditioning system in accordance with claim 1 wherein said heat exchange medium will be supplied to said condenser in response to a predetermined thermal condition within said refrigeration unit, while said compressor is inoperable and at a time when the thermal condition of the area being served does not require operation of the refrigeration unit.

5. A control circuit for an air conditioning system including a refrigeration unit comprising a motor-driven compressor, a condenser, an evaporator, and expansion means, said expansion means dividing said refrigeration unit into a high pressure side and a low pressure side, said control circuit comprising:

-(A) a supply circuit for providing electrical energy to a compressor motor including (i) a controller including a first switch for connecting said motor to said supply circuit, said controller including an energizing coil;

(B) thermally responsive switch means regulating operation of the control circuit;

(C) a supply circuit for providing electrical energy to operate means for furnishing a heat exchange medium to the condenser of said air conditioning system, said supply circuit being independently operable from said compressor motor supply circuit so that said heat exchange medium can be supplied to said condenser even though said compressor motor circuit is inoperable; and

(D) pressure responsive means operable when a pressure dilferential between the high pressure side and the low pressure side of said refrigeration unit exceeds a predetermined point to prevent said compressor motor from becoming operable until said pressure diiferential has been reduced to said predetermined point, said pressure responsive means being inoperable upon energization of said compressor motor.

6. A control circuit in accordance with claim 5 wherein said supply circuit for operating means furnishing a heat exchange medium to said condenser will additionally operate means to supply a heat exchange medium to said evaporator.

7. A control circuit in accordance with claim 5 wherein said heat exchange medium is ambient air and said heat exchange medium supply means is a motor-driven fan.

8. A control circuit for an air conditioning system in accordance with claim 5 wherein said heat exchange rnedium supply circuit will include means responsive to the thermal condition of said refrigeration unit and means responsive to the thermal condition of the area being served by said refrigeration unit, said means being independently operable to energize said supply circuit.

References Cited UNITED STATES PATENTS 1,886,607 11/1932 Deventer 62-181 2,847,831 8/1958 Carraway 62-151 3,110,160 11/1963 Miner 62-209 3,358,468 12/1967 Shaw 62-158 MEYER PERLIN, Primary Examiner U.S. Cl. X.R. 

